Activation and regeneration of fluorination catalysts, and fluorination process

ABSTRACT

A fluorination catalyst such as a chromium oxide-based fluorination catalyst may be activated or reactivated by contacting the catalyst. with a source of reactive fluorine, for example nitrogen trifluoride (NF3) or fluorine (F2). Fluorinated compounds may be prepared by the gas phase reaction of hydrogen fluoride (HF) with various substrates such as chlorinated compounds. A number of metal oxide-based catalysts have been developed for this purpose.

This present application is the national phase under 35 USC § 371 ofprior PCT International Application Number PCT/US2014/012166 filed Jan.20, 2014 which designated the United States of America and claimedpriority to U.S. Provisional Patent Application Ser. No. 61/757,768filed Jan. 29, 2013.

FIELD OF THE INVENTION

The invention relates to methods for activating and regeneratingcatalysts used to fluorinate substrates such as chlorinated compoundsusing hydrogen fluoride.

BACKGROUND OF THE INVENTION

Fluorinated compounds may be prepared by the gas phase reaction ofhydrogen fluoride (HF) with various substrates such as chlorinatedcompounds. A number of metal oxide-based catalysts have been developedfor this purpose. However, such catalysts typically lose activity withprolonged use. Additionally, inactive catalyst precursors often must beactivated in order to prepare such fluorination catalysts.

Various methods for activating and reactivating metal oxide-basedfluorination catalysts, as well as methods for extending the useful lifeof such catalysts, have been investigated. However, these methods areknown to possess certain disadvantages. For example, oxygen (O₂) may beco-fed continuously or intermittently during the fluorination reactionor during reactivation for the purpose of oxidizing and removingcarbonaceous deposits, which tend to inhibit catalyst activity, from thecatalyst surface. However, water and carbon dioxide typically areproduced as by-products. The water generated may itself damage anddeactivate the catalyst due to phase changes triggered by the repeatedaddition and loss of water from the catalyst. The presence of water inthe reactor system may also lead to corrosion or erosion of fluorinationequipment.

Accordingly, the development of improved, effective procedures for bothactivating and reactivating catalysts for use in fluorination reactionswhich avoid the generation of water would be of interest.

SUMMARY OF THE INVENTION

One aspect of the invention provides a method of reactivating a spent ordepleted fluorination catalyst (in particular, a metal oxide-basedfluorination catalyst such as a chromium oxide-based fluorinationcatalyst), comprising contacting the spent or depleted fluorinationcatalyst with an agent that is a source of reactive fluorine such as NF₃or F₂. The fluorination catalyst may have been used to catalyze thefluorination of a chlorinated compound such as a chloroolefin orchloroalkane using HF. The contacting may be carried out in a gas(vapor) phase at a temperature of about 100° C. to about 400° C., forexample.

Another aspect of the invention furnishes a fluorination process,alternately comprising reaction stages and regeneration stages, whereinthe reaction stages comprise reacting a compound with HF in a gas phasein the presence of a fluorination catalyst to produce a fluorinatedcompound and the regeneration stages comprise contacting thefluorination catalyst with an agent that is a source of reactivefluorine such as NF₃ or F₂. Such a process may additionally comprise apreliminary activation stage which comprises contacting a fluorinationcatalyst precursor with an agent that is a source of reactivefluorinesuch as NF₃ or F₂.

A method of activating a fluorination catalyst is additionally suppliedby the invention, comprising contacting a fluorination catalystprecursor with an agent that is a source of reactive fluorine such asNF₃ or F₂. The contacting may, for example, be carried in a gas phase ata temperature of about 100° C. to about 400° C.

The activation and reactivation processes of the present invention maybe carried out in situ (i.e., the catalyst may be activated orreactivated while in place in the equipment used for fluorination of asubstrate) or ex situ (i.e., the catalyst may be activated orreactivated in accordance with the invention in equipment other than thefluorination equipment and subsequently transferred to the fluorinationequipment).

DETAILED DESCRIPTION OF THE INVENTION

Activation/Reactivation Agents

The present invention utilizes a source of reactive fluorine such asnitrogen trifluoride (NF₃) or fluorine (F₂) or mixtures thereof as anagent for activating and/or reactivating fluorination catalysts. Suchagents are fluorine-containing substances other than HF which arecapable of supplying fluorine in a form which reacts with the catalystso as to increase or restore its catalytic activity. Other useful agentsfor such purposes may include, for example, interhalogens (e.g., ClF,ClF₃, ClF₅, BrF₃, BrF₅, IF₅, and IF₇); hypofluorites (e.g., CF₃OF);fluorinated peroxides such as CF₃OOCF₃, as well as other fluoride andoxide fluoride compounds such as OF₂, O₂F₂, N₂F₂, N₂F₄, SF₄, SOF₄, SOF₂,XeF₂, XeF₄, XeF₆, KrF₂, FNO, FNO₂, and FClO₃.

The catalyst activation/reactivation agent may be admixed with one ormore other substances as it is contacted with the catalyst precursor ordeactivated catalyst. For example, the agent(s) which serve as a sourceof reactive fluorine may be present in combination with one or more ofHF, HCl, chlorocarbons, fluorocarbons, O₂, N₂, CO, CO₂ and the like.Particular examples of such admixtures include, but are not limited to:HF+NF₃; HF+HCl+NF₃; HF+chlorocarbons+NF₃; and O₂+NF₃. Such admixturesmay be obtained as a result of recycling the stream containing theactivation/reactivation agent after the agent is passed over or throughthe catalyst.

Fluorination Reaction

In the fluorination reaction of the invention, a substrate such as achlorinated compound is converted to a fluorinated compound through areaction with hydrogen fluoride (HF) in the presence of a metaloxide-based catalyst. Where the substrate is a halogenated compound suchas a chlorinated compound, the substrate may undergo a halogen exchangereaction catalyzed by the metal oxide-based catalyst (e.g., F issubstituted for Cl). The “chlorinated compound” can be any moleculehaving at least one chlorine atom, and the “fluorinated compound” can beany molecule having at least one fluorine atom. The fluorinationreaction may involve a reaction other than a halogen exchange reaction.For example, a fluorine atom may be substituted (exchanged) for ahydrogen atom on the substrate.

In one embodiment of the invention, the chlorinated compound is a C1 toC8 alkane or alkene compound, which may be linear or branched, havingone or more substituents selected from F, Cl, I and Br, with at leastone of the substituents being Cl. Mixtures of such chlorinated compoundsmay also be used. The fluorinated compound may be a C1 to C8 alkane oralkene compound, which may be linear or branched, having one or moresubstituents selected from F, Cl, I and Br, at least one of thesubstituents being F. Mixtures of such fluorinated compounds may beproduced.

In one particular embodiment, the chlorinated compound is a C3 alkane oralkene compound having one or more substituents selected from F, Cl, Iand Br, at least one of the substituents being Cl; and the fluorinatedcompound is a C3 alkene compound having one or more substituentsselected from F, Cl, I and Br, at least one of the substituents being F.Alternatively, the chlorinated compound can be a C4 alkane or alkenecompound having one or more substituents selected from F, Cl, I and Br,at least one of the substituents being Cl; and the fluorinated compoundis a C4 alkene compound having one or more substituents selected from F,Cl, I and Br, at least one of the substituents being F. According to oneembodiment, the fluorinated compound is a hydrofluorolefin (and thus hasno chlorine substituent). Typically, during the reaction at least one Clsubstituent in the chlorinated compound is replaced by an F substituent.

The conversion of the chlorinated compound to the fluorinated compoundmay comprise direct conversion (i.e. in a single reaction step or underessentially one set of reaction conditions) or indirect conversion(i.e., through two or more reaction steps or using more than one singleset of reaction conditions).

Illustrative fluorination reactions in accordance with the inventioninclude the following:

2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf) to2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);

1,1,1,2,3-pentachloropropane (HCC-240db) to2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);

1,1,2,2,3-pentachloropropane (HCC-240aa) to2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);

2,3-dichloro-1,1,1-trifluoropropane (HCFC-243db) to2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);

1,1,2,3 tetrachloro-1-propene (HCO-1230xa) to2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);

2,3,3,3 tetrachloro-1-propene (HCO-1230xf) to2,3,3,3-tetrafluoro-1-propene (HFO-1234yf);

1,1,1,2,3-pentachloropropane (HCC-240db) to2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf);

1,1,2,2,3-pentachloropropane (HCC-240aa) to2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf);

2,3-dichloro-1,1,1-trifluoropropane (HCFC-243db) to2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf);

1,1,2,3 tetrachloro-1-propene (HCO-1230xa) to2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf);

2,3,3,3 tetrachloro-1-propene (HCO-1230xf) to2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf).

The fluorination reaction can be carried out with an HF molar ratio ofHF to compound to be fluorinated typically from 3:1 to 150:1, at acontact time from 6 to 100 s and a pressure from atmospheric pressure to20 bars. The catalyst bed temperature can be, for example, from 100 to450° C.

Catalyst

The fluorination catalyst used in the present invention can be supportedor unsupported. It can be, for example, a catalyst based on a metalincluding a transition metal oxide or a derivative thereof. In oneembodiment, the catalyst is a chromium oxide-based catalyst. Suitablecatalysts include, but are not limited to, metal oxide-based bulk andsupported catalysts, including doped and undoped catalysts. A catalystprecursor to be activated in accordance with one aspect of the inventionmay be any metal oxide (e.g., corresponding to the general empiricalformula MxOy, wherein x is 1-2 and y is selected such that the valencyof M is satisfied). The metal M may be, for example, a first or secondrow transition metal. Once activated, the catalyst may be a metal oxidefluoride corresponding to the general empirical formula MxOyFz, whereinx is 1-2 and y and z are selected such that the valency of M issatisfied. When M is chromium (Cr), the valency of M is typically 3-6.

The metal in the catalyst is converted to metal derivatives duringactivation (or regeneration), including oxides, halides or oxidehalides. The metals in the catalyst are typically present in the form ofmetal oxides, oxychlorides, chlorides, chlorofluorides,oxychlorofluorides, oxyfluorides or fluorides. Thus, when thefluorination catalyst is a chromium oxide-based catalyst, the catalysttypically contains an oxide, oxide halide (for example, an oxyfluoride)and/or halide of chromium (for example, a fluoride of chromium).

A particularly suitable catalyst for use in the present invention is ahigh surface area unsupported chromium oxide-based catalyst. However,supported chromium oxide-based catalysts are also suitable for use.

The catalyst can optionally contain a low level of one or moreco-catalysts (sometimes referred to as dopants) such as Co, Zn, Mn, Mg,V, Mo, Te, Nb, Sb, Ta, P, Ni, Ca, Sr, Ba, Na, K, Rb, Cs, Cd, Hg, Cu, Ag,Au, Pd, Pt, W, Ti, Zr, and/or Hf.

In one embodiment of the invention, the fluorination catalyst is anunsupported chromium catalyst which can optionally contain low levels ofone or more co-catalysts selected from cobalt, nickel, zinc ormanganese, prepared by processes known in the art, such as impregnation,mixed powder, co-precipitation and the like.

The amount of co-catalyst, when present, can be varied between 1 to 10wt %, e.g., between 1 to 5 wt %. The co-catalyst can be added to thecatalyst by processes known in the art such as adsorption from anaqueous or organic solution, followed by solvent evaporation.

The catalyst precursor, before activation, may be subjected to a dryingstep, such as a step which comprises passing a drying gas, such asnitrogen, over the catalyst precursor. The drying step can be carriedout at a pressure of from atmospheric pressure up to 20 bars, forexample. The temperature of the catalyst precursor during the dryingstep can range from room temperature up to 400° C., e.g., from about175° C. to about 275° C. with a volumetric flow rate of the activatingagent corresponding to a contact time in the catalyst bed of from about1 to 100 s, e.g., from about 10 to 40 s, for an activation duration offrom about 0.5 to 50 hours, e.g., between 1 to 5 hours. After the dryingstep, the catalyst precursor needs to be activated (i.e., converted to asubstance having high catalytic activity for the fluorination of asubstrate such as a chlorinated compound using HF).

Activation of the Catalyst

The present inventors have found that the activation of the abovecatalysts using an agent that is a source of reactive fluorine such asNF₃ and/or F₂ makes it possible to significantly improve the efficiencyof the fluorination process. The activation process may compriseactivating the catalyst precursor using at least one activating agent.The temperature of this activation step can range from about 100 toabout 500° C., e.g., from about 300 to about 400° C., with a volumetricflow rate of the activating agent corresponding to a contact time in thecatalyst bed of from about 1 to about 200 s, for an activation durationof from about 10 to about 300 hours.

The above activation processes can be carried out at a pressure of fromatmospheric pressure up to about 20 bars. The activating agent can befed to the system with an inert gas such as nitrogen. The proportion ofactivating agent can range from about 1 to 100 mole % of the mixture. Inone embodiment, NF₃ is employed as the activating agent and is contactedwith the catalyst precursor in pure or essentially pure form (i.e., NF₃comprises from 90 to 100 mole % of the gas contacted with the catalystprecursor).

Regeneration (Reactivation) of the Catalyst

The present inventors have also found that the efficiency of thefluorination reaction tends to decrease over time, but that it can beincreased again up to, and even above, the initial efficiency, bysubjecting the catalyst to regeneration stages wherein it is contactedwith an agent that is a source of reactive fluorine such as NF₃ or F₂,in a similar way as during the initial activation stage. The temperatureduring the regeneration step can range from about 100 to about 500° C.,with a contact time of from about 1 to about 200 s, for about 1 to about200 hours. The regeneration step can be carried out at a pressure fromatmospheric pressure to about 20 bars. The reactivating agent can be fedto the system with an inert gas such as nitrogen. The proportion ofreactivating agent can range from about 1 to about 100 mole % of themixture. In one embodiment, NF₃ is employed as the reactivating agentand is contacted with the spent catalyst in pure or essentially pureform (i.e., NF₃ comprises from 90 to 100 mole % of the gas contactedwith the spent catalyst).

When reaction stages alternate with regeneration stages, the duration ofeach reaction stage can be from 50 to 2000 hours, e.g., from 200 to 1000hours, and the duration of each regeneration stage can be from 1 to 200hours, e.g., from 2 to 20 hours.

EXAMPLES Example 1: Activation with Pure NF₃

Pellets of chromium oxide (Cr₂O₃) doped with Zn were crushed and sievedto uniform particle size of 8 to 20 mesh. A 1″ o.d. tubular reactor wasloaded with a bed containing 46 cc (40.65 g=268 mmol) of the sizedcatalyst precursor. The bed was heated to 225° C. and flushed with dryN₂ for 2.5 hours to facilitate removal of volatiles. The bed was thenheated to 350° C. and pure NF₃ was flowed through the bed atapproximately 5 sccm for 24 hours. After the specified time, NF₃ flowwas terminated and replaced by 100 sccm dry N₂. Nitrogen was flowed forapproximately 72 hours. After the specified time, N₂ was replaced by areactant mixture consisting of HF, air, and3,3,3-trifluoro-2-chloropropene, (CF₃C(Cl)═CH₂, hereafter called1233xf), flowing at ambient pressure with a contact time of 20 secondsthrough the catalyst bed heated to 350° C. The mixture containedreactants in the molar ratio HF:1233xf:O₂=20:1:0.2.

The product exiting the reactor was passed through a caustic scrubberand analyzed subsequently online by gas chromatography (GC). Initialconversion of 1233xf was approximately 56% with steady-state selectivityof 73% 2,3,3,3-tetrafluoropropene (hereafter called 1234yf) and 23%1,1,1,3,3-pentafluoropropane (hereafter called 245cb). The reactantmixture was flowed continuously for approximately 100 hours after whichthe reactant mixture was replaced by N₂ for a period of 10 days.Following the 10 day purge with N₂, the reactant mixture was resumed asbefore and continued for an additional 250 hours. During these 250 hoursthe conversion declined slowly from approximately 50% to a steady-statevalue of 23%. Selectivity remained at 73% 1234yf and 23% 245cb. Afterthis 250 hour reaction period the catalyst was deemed “deactivated” asit was at its lowest 1233xf conversion rate. The catalyst bed was heldat 350° C. and purged with N₂ for 4 days before being used in Example 2.

Example 2: Reactivation of Deactivated Catalyst with Pure NF₃

The deactivated catalyst remaining at the end of Example 1 wasreactivated with pure NF₃ as follows. Pure NF₃ was flowed atapproximately 5 sccm through the depleted bed for 22 hours at 350° C.During the reactivation with NF₃ an exotherm was observed in the bedduring the initial few hours. In addition, volatile products of thereactivation process were observed by online GC analysis only during thefirst 293 minutes of activation, after which just NF₃ was observedflowing from the bed.

Following the 22 hour reactivation period, the pure NF₃ flow wasreplaced by a reactant mixture similar to that described in Example 1(HF:1233xf:O₂=20:1:0.2), flowing at ambient pressure with a contact timeof 20 seconds through the catalyst bed heated to 350° C.

The product exiting the reactor was passed through a caustic scrubberand analyzed online by gas chromatography (GC). Initial conversion of1233xf was approximately 60% with steady-state selectivity of 70% 1234yfand 28% 245cb. The reactant mixture was flowed continuously forapproximately 100 hours after which the reactant mixture was replaced byN₂ for a period of 3 days.

Example 3: Activation Using NF₃ Followed by Air

Pellets of chromium oxide (Cr₂O₃) doped with Zn were crushed and sievedto uniform particle size of 8 to 20 mesh. A 1″ o.d. tubular reactor wasloaded with a bed containing 100 cc (94.9 g=624 mmol) of the sizedcatalyst precursor. The bed was heated to 275° C. and flushed with pureN₂ for 72 hours to facilitate removal of volatiles. The flow of pure N₂was replaced with a mixture containing 5 sccm pure NF₃ and 100 sccm pureN₂ and this flow was continued for approximately 24 hours. The bedtemperature was then raised to 350° C. and pure NF₃ was added at 5 sccmuntil approximately 642 mmol total NF₃ had been added. Following theaddition of NF₃, air was added at 25 sccm for a period of 4 days at 350°C. and at ambient pressure. After the specified time the flow of air wasreplaced by a reactant mixture similar to that described in Example 1with the exception that 4% O₂ was used (HF:1233xf:O₂=20:1:0.04). Thereactant mixture was flowed continuously at 1 bar absolute pressure witha contact time of 20 seconds through the catalyst bed heated to 350° C.

The product exiting the reactor was passed through a caustic scrubberand analyzed subsequently online by gas chromatography (GC). Initialconversion of 1233xf was approximately 58% with steady-state selectivityduring the first 90 hours of reaction of 73% 1234yf and 25% 245cb. Thereactant mixture was flowed continuously for approximately 90 hoursafter which the reactant mixture was replaced by air for a period of 10days. Following the 10 day reactivation with air, the reactant mixturewas resumed as before and continued for an additional 260 hours. Duringthe 260 hour reaction period the conversion declined slowly fromapproximately 65% to about 30% while the selectivities varied from 33%to 50% for 1234yf and from 62% to 47% for 245cb. Following the 260 hourreaction period the reactant mixture was replaced by air for a 3 dayreactivation. Following reactivation, feeding of the reactant mixturewas resumed as before and continued for an additional 400 hours. Duringthe 400 hour reaction period the conversion declined slowly fromapproximately 65% to about 35% while the selectivities varied from 35%to 40% for 1234yf and from 62% to 57% for 245cb. Following the 400 hourreaction period the experiment was terminated.

Example 4: Attempted Activation Using Air and NF₃

Pellets of chromium oxide (Cr₂O₃) doped with Zn were crushed and sievedto uniform particle size of 8 to 20 mesh. A 1″ o.d. tubular reactor wasloaded with a bed containing 23 cc (20.74 g=140 mmol) of the sizedcatalyst precursor. The bed was heated to 325° C. and flushed with pureair for 3 hours to facilitate removal of volatiles. The flow of pure airwas replaced with a mixture containing 5 sccm pure NF₃ and 75 sccm pureair; however, an exotherm was observed so the flows were reduced to 0.5sccm pure NF₃ and 7.5 sccm pure air. The bed pressure was increased fromambient to approximately 37 psig. The mixture of NF₃ and air wascontinued until approximately 500 mmol NF₃ had been added. After thespecified time, the flow of NF₃ and air was replaced by a reactantmixture similar to that described in Example 1 (HF:1233xf:O₂=20:1:0.2)),flowing at 3.5 bar absolute pressure with a contact time of 20 secondsthrough the catalyst bed heated to 350° C.

The product exiting the reactor was passed through a caustic scrubberand analyzed subsequently online by gas chromatography (GC); however, itwas determined that little if any 1233xf was converted to products. Atthis point, the reactant mixture was replaced for a short period by NF₃followed by air followed by a flow of air that was continued for 4 days.After the specified time, the air was replaced with the reactantmixture; however, the 1233xf conversion was <10% and as such, thecatalyst was deemed “not activated.”

Example 5: Activation Under Pressure Using NF₃ Followed by Air

Pellets of chromium oxide (Cr₂O₃) doped with Zn were crushed and sievedto uniform particle size of 8 to 20 mesh. A 1″ o.d. tubular reactor wasloaded with a bed containing 46 cc (40.11 g=264 mmol) of the sizedcatalyst precursor. The bed was heated to 200° C. and flushed with pureN₂ to facilitate removal of volatiles. The flow of N₂ was replaced witha mixture at ambient pressure containing, initially, 5 sccm pure NF₃ and20 sccm N₂ which was replaced ultimately with pure NF₃ flowing at 5 sccmand at 3.5 bar absolute pressure for the duration of the NF₃ addition.In total, about 10 mol % excess NF₃ was used. After the addition of NF₃was terminated, pure air was flowed at 350° C. and 3.5 bar absolutepressure for a period of 6 days. After the specified time the flow ofair was replaced by a reactant mixture similar to that described inExample 1 (HF:1233xf:O₂=20:1:0.2)), flowing at 3.5 bar absolute pressurewith a contact time of 20 seconds through the catalyst bed heated to350° C.

The product exiting the reactor was passed through a caustic scrubberand analyzed subsequently online by gas chromatography (GC). Initialconversion of 1233xf was approximately 36% but declined steadily overthe course of the first 70 hours to a final value <10%. The steady-stateselectivities reached during the first 70 hours of reaction were 65%1234yf and 25% 245cb. The reactant mixture was flowed continuously forapproximately 70 hours after which the reactant mixture was replaced byair for a period of 3 days. Following the 3 day reactivation attemptwith air, feeding of the reactant mixture was resumed as before;however, the conversion declined rapidly from about 30% to about 10%over a period of about 50 hours and thus the catalyst was deemed notadequately activated and the experiment was terminated.

What is claimed is:
 1. A method of reactivating a spent or depletedchromium oxide-based fluorination catalyst, comprising contacting thespent or depleted chromium oxide-based fluorination catalyst with anagent that is a source of reactive fluorine selected from the groupconsisting of interhalogens, hypofluorites, fluorinated peroxides, OF₂,O₂F₂, N₂F₂, N₂F₄, SOF₄, SOF₂, XeF₂, XeF₄, XeF₆, KrF₂, FNO, FNO₂, FClO₃,and mixtures thereof.
 2. The method of claim 1, wherein the chromiumoxide-based fluorination catalyst is a bulk (unsupported) or supportedchromium oxide-based fluorination catalyst.
 3. The method of claim 1,wherein the fluorination catalyst has been used to catalyze thefluorination of a chloroolefin or chloroalkane using HF.
 4. The methodof claim 1, wherein the contacting is carried in a gas phase at atemperature of about 330° C. to about 400° C.
 5. A method of activatinga chromium oxide-based fluorination catalyst, comprising contacting achromium oxide-based fluorination catalyst precursor with an agent thatis a source of reactive fluorine selected from the group consisting ofinterhalogens, hypofluorites, fluorinated peroxides, OF₂, O₂F₂, N₂F₂,N₂F₄, SOF₄, SOF₂, XeF₂, XeF₄, XeF₆, KrF₂, FNO, FNO₂, FClO₃, and mixturesthereof.
 6. The method of claim 5, wherein the chromium oxide-basedfluorination catalyst precursor is comprised of bulk (unsupported) orsupported chromium oxide.
 7. The method of claim 5, wherein thecontacting is carried in a gas phase at a temperature of about 300° C.to about 400° C.
 8. A fluorination process, alternately comprisingreaction stages and regeneration stages, wherein the reaction stagescomprise reacting a compound with HF in gas phase in the presence of achromium oxide-based fluorination catalyst to produce a fluorinatedcompound and the regeneration stages comprise contacting thefluorination catalyst with an agent that is a source of reactivefluorine selected from the group consisting of interhalogens,hypofluorites, fluorinated peroxides, OF₂, O₂F₂, N₂F₂, N₂F₄, SF₄, SOF₄,SOF₂, XeF₂, XeF₄, XeF₆, KrF₂, FNO, FNO₂, FClO₃, and mixtures thereof. 9.The fluorination process of claim 8, wherein the chromium oxide-basedfluorination catalyst is a bulk (unsupported) or supported chromiumoxide-based fluorination catalyst.
 10. The fluorination process of claim8, additionally comprising a preliminary activation stage whichcomprises contacting a fluorination catalyst precursor with an agentthat is a source of reactive fluorine.